The invention relates to a viscous coupling having a housing and at least one hub rotatably supported therein and relatively thereto. The coupling also has sets of plates which are associated with the housing and the hub(s), which are arranged in a certain sequence and which comprise apertures. The plates associated with the housing or hub(s) are provided with index recesses for assembly purposes. Additionally, a viscous medium, especially silicone oil, at least partially fills the internal space which remains between the housing and the hub(s) and which is not occupied by plates.
In the case of viscous couplings, it is known to provide the outer plates associated with the housing with two diametrically opposed index recesses which serve to align the plates in their positions relative to each other.
Depending on the application of viscous couplings which, above all, are used in vehicle construction, the plates have to be differently assembled relative to each other. For example, with viscous couplings used in the driveline between the front and rear wheels of a four wheel drive vehicle it is necessary for the slots of the outer plates arranged in the housing in an axial sequence to be offset relative to each other in the circumferential direction, thereby forming a kind of labyrinth to facilitate the transfer of the coupling into the so-called hump mode. However, with different applications it is necessary to achieve different characteristics of the torque/speed curve. For instance, a 100% torque transmission is to be avoided; only part of the input torque is to be transmitted.
With such a viscous coupling design, the apertures of the slots have to be aligned so that their positions correspond to each other.
However, with the prior art design there is a problem in that there exist no accurate means of checking whether the specified assembly sequence and alignment of the plates have actually been observed.